Concept Tests Final Review Quiz for the arrogant physicist Name a commonly occurring physical phenomenon which remains completely mysterious despite many decades of intense study We have no equations which describe it no theory which explains it We are not even sure how to measure it CTF 1 How many A in a mA A 10 B 1000 C 100 000 Answer 1000 micro amp A 10 6 A D 1 000 000 milli amp mA 10 3 A CTF 2Calculator question 105 A 1E5 B 10E5 C something else Answer 1E5 1 105 CTF 3 A square with edge length L is made larger and larger As the square grows the ratio A increases Answer length of perimeter B decreases area C remains constant length 4 L 4 2 The ratio decrease as L increases area L L CTF 4 A charge q is released from rest at point in empty space were there may be E and or B fields There are no forces on the charge except for the forces due to the E and or B fields no gravity etc The charge is observed for a short while and is seen to move along a curved path Which one statement must be true q A There might be only a non zero E field present and no B field B There might be only a non zero B field present and no E field C There must be both a non zero E field and a non zero B field present D None of the above statements must be true Answer This is a very tricky problem trickier than what I would give on the Final You have to distinguish carefully between the words might and must The correct answer is There might be only a non zero E field present and no B field If the particle is in a curved E field it will accelerate along a curved path It is true that this path could be caused by a B and E field acting together but it is not true that the path must be caused by a B and E field together CTF 5 Points A and B are distances r and 2r respectively from a point charge q What is the magnitude of the voltage difference V VB VA r q r A A kq r C 3 kq 2 r B B 1 kq 2 r D None of these kq kq 1 kq The question asks for the magnitude of 2r r 2 r the voltage difference so we drop the minus sign Answer V VB VA CTF 6 A charge q is located at the center of an gaussian cubical box as shown A student is asked What is the electric flux E though the top face of the cube Is the answer hard to calculate or easy to calculate q A Easy B Hard r r Qinside E dA Answer Its easy if you remember Gauss s Law The total flux through eo the entire box is q o By symmetry the flux through one face is 1 6 th the flux through the whole box Flux 1 6 q o CTF 7 A capacitor with capacitance C is attached to a battery with voltage V What is the flux z E da through the cubical volume shown The end faces of the cube are within the metal plates of the capacitor C A CV o B 2CV o C zero D None of these V Answer Zero In electrostatic situations the E field inside a conductor is zero Since E 0 on the right and left ends of the imaginary cubical box the flux through those ends is zero On the sides of the box E da 0 since E da So the total flux is zero Since z E da 0 then by Gauss s Law the total charge must be zero within the box must be zero so we have proven that the two plates must have equal and opposite charge densities CTF 8 A resistor is plugged into a 120VAC wall socket The graph below is either voltage V across current I in or power P dissipated in the resistor vs time time What could the graph be A V only B I only D V I or P E something else C V or I only Answer V or I only The power P IV I2R is always positive P time I or V CTF 9 A capacitor has a voltage V across its plates An electron initially at rest is released from a point very close to the negative plate of a capacitor and it accelerates toward the positive plate The electron has charge e and mass m There is no gravity in this problem and you may assume that the motion of the electron is non relativistic What is the final speed of the electron just before it collides with the positive plate A 2 e V m B C 2 e V m D m e V m 2 e V E None of these V Answer 2 e V m 1 KE PE mv 2 e V 2 CTF 10 When the switch is closed the current I1 through resistor R1 I bat A increases B decreases C stays the same V R1 I1 R2 Answer stays the same The resistor R1 is attached to the battery with constant voltage V Ohm s Law says V I1 R1 Regardless of whether the switch is open or closed the current thru R 1 is I1 V R1 What changes when the switch is closed is the total current thru the battery Itot I1 I2 CTF 11 At time to a particle with charge q has instantaneous velocity in moving in a uniform magnetic field v o as shown and B B x A True or B False As time increases the xcomponent of the velocity vx remains constant V B q Answer True the force F qv B is into or out of the page depending on the sign of q The direction of the force is perpendicular to the x axis the direction of B so Fx max 0 ax 0 means vx constant A True or B False The KE of the particle remains constant as time increases r r True The magnetic field can do no work on the particle since F v always The KE can change only if work is done by the work energy theorem KE Wnet CTF 12 A long solenoid with many turns per length has a uniform magnetic field B within its interior Consider the imaginary rectangular path of length c and width a with one edge entirely within the solenoid as shown c a What is A Bc z B dl B 2B c a C 2Bc B D None of these The solenoid has n turns per length and carries a current I What is A o nI B o ncI C o n a c I z B dl D None of these Answer the bottom of the loop contributes to the line integral On the sides …
View Full Document
Unlocking...